Due to its characteristics of being easily applicable to various products and electrical properties such as a high energy density, a secondary battery is not only commonly applied to a portable device, but universally applied to an electric vehicle (EV) or a hybrid electric vehicle (HEV) and an energy storage system that drive by an electric driving source. This secondary battery is gaining attention for its primary advantage of remarkably reducing the use of fossil fuels and not generating by-products from the use of energy, making it a new eco-friendly and energy efficient source of energy.
A battery pack for use in electric vehicles has a structure consisting of a plurality of cell assemblies connected in series, each cell assembly including a plurality of unit cells, to obtain high power. Also, the unit cell includes a positive electrode current collector and a negative electrode current collector, a separator, an active material, and an electrolyte solution, and allows repeated charging and discharging by electrochemical reactions between the constituent elements.
Recently, with the growing need for a high-capacity structure as well as utilization as an energy storage source, there is an increase in demand for a battery pack with a multi-module structure in which a plurality of battery modules including a plurality of secondary batteries connected in series and/or in parallel are assembled.
Because a battery pack with a multi-module structure is designed to include a plurality of secondary batteries arranged with a high density in a narrow space, it is important to easily emit heat generated from the respective secondary batteries. Because charging and discharging of secondary batteries are accomplished by electrochemical reactions as noted above, unless heat generated during charging and discharging is effectively removed from a battery module, heat accumulation occurs and as a result, degradation of the battery module is accelerated, and in some instances, a fire or explosion may occur.
Accordingly, a high-output high-capacity battery module and a battery pack with the same necessarily need a cooling device to cool down battery cells embedded therein.
Generally, a cooling device is typically classified into two types: an air-cooled cooling type and a water-cooled type, and an air-cooled cooling type is being used more widely than a water-cooled type due to short circuits or a waterproof problem of secondary batteries.
FIG. 1 is a schematic perspective view of a battery module according to a related art.
Because an amount of power produced by one secondary battery cell is not high, a commercially available secondary battery includes a stack of as many secondary battery cells 3 as needed. Also, as shown in FIG. 1, to properly maintain the temperature of the secondary battery by cooling the heat generated during the production of electricity from the unit cells 3 of the secondary battery, cooling fins 2 are inserted between the cells 3. The cooling fin 2 having absorbed heat from each unit cell 3 transmits the heat to a heat sink 1, and the heat sink 1 is cooled by cooling water or cool air. In this instance, a member for reducing thermal contact resistance, such as a thermal interface material (TIM) 4, may be further added between the cooling fin 2 and the heat sink 1.
However, this cooling fin 2 according to the related art has low thermal conductivity due to contact resistance with the heat sink 1, failing to smoothly discharge heat generated from the secondary battery cells.